Global navigation satellite systems (GNSS), such as the Global Positioning System (GPS), Galileo and the like, generally rely on a terrestrial navigation receiver to process signals from a satellite position system (“SPS signals”). The SPS signals are usually transmitted from transmitters fixed to space vehicles (SVs) to obtain pseudo-range measurements from the terrestrial navigation receiver to the transmitters.
In many instances, the terrestrial navigation receiver may need to overcome undesired radio frequency (RF) energy in the form of radio-frequency-interference (RFI) or “spurs.” The spurs take the form of narrow-band frequency signals that may result from in-band or out-of-band noise sources.
One proposed method of handling spurs involves detecting the spurs and programming spur cancellation circuits to cancel the spurs. This may be an effective way to remove the spurs. However, over time the spurs may exhibit changes in characteristics such as an offset in frequency or variable strength and bandwidth.